1. Field of the Invention
The present invention relates generally to the field of xerographic printing. More specifically, the present invention discloses a device to assist in properly orienting the magnetic brush in the developer station of a xerographic printer.
2. Statement of the Problem
Conventional xerographic copiers and printers reproduce images by creating a latent electrostatic image on a rotating print drum having a photoconductive surface. Following exposure, the latent electrostatic image on the print drum is developed at a developing station which in typical present day practice, comprises one or more magnetic brushes for bringing a developer in powder form, usually a mixture of carrier beads and toner, into developing relation with the surface of the print drum and the image thereon. This is conventionally accomplished by a developer roll having thin, cylindrical outer wall which is rotatably mounted parallel to the print drum. The lower portion of the developer roll passes through a sump containing the developer. A thin layer of developer adheres to the outer surface of the developer roll as it rotates. A small spacing is maintained between the developer roll and the print drum. A number of stationery magnetic brushes extend longitudinally within the developer roll adjacent to the line of minimum spacing between the print drum and developer roll. The lines of force created by the magnetic brushes pass through the wall of the developer roll and cause the developer particles to stand on end, similar to the way in which iron filings align themselves to follow the lines of force of a magnetic field. This alignment of the developer particles by the magnetic brushes causes them to bridge the gap separating the developer roll from the print drum, and thereby be applied to the latent image on the print drum. Following application of the developer, the developed image is transferred at a transfer station to a copy substrate material such as a sheet of paper. Print quality is adversely affected if the proper angular relationship between the print drum and the magnetic brushes within the developer roll is not maintained. The developer roll typically provides some means to permit small adjustments in the angular position of the magnetic brushes. However, heretofore, adjustment of this angular relationship to achieve optimal print quality has largely been a matter of trial and error.
The prior art contains several other examples of xerographic copiers and printers which use a magnetic brush within a developer roll to apply developer to the print drum, including the following:
______________________________________ Inventor U.S. Pat. No. Issue Date ______________________________________ Harlow, et al. 4,250,513 Feb. 10, 1981 Suzuki 4,334,772 June 15, 1982 Daniels 4,439,034 Mar. 27, 1984 Jugle 4,466,730 Aug. 21, 1984 Dolan 4,470,693 Sep. 11, 1984 Manno 4,690,540 Sep. 1, 1987 ______________________________________
Harlow, et al., disclose a linear vertical adjustment mechanism for a printer. This device has particular application to align an ink or toner applicator member, such as a magnetic ink brush, with respect to a recording medium to insure that the magnetic brush is parallel to the recording medium, and thereby prevent variation in the print intensity across the width of the print medium.
Suzuki discloses an electrophotographic apparatus having a magnetic brush assembly that is somewhat similar to the magnetic brush assembly found in the types of printer that can be adjusted using the present invention.
Daniels discloses a method and apparatus for purging developer mix from the magnetic brush roller by rotating the magnets of the magnetic brush roller.
Jugle discloses an electrophotographic apparatus in which the amount of developer material being transported to the electrostatic latent image recorded on the photoconductive belt is controlled by a metering blade. The accumulation of surplus toner particles on the blade is prevented by inducing a flow of air through apertures in the blade.
Dolan discloses a self-cleaning xerographic apparatus in which the magnetic brush is used to both apply toner to an image on a photoconductive surface and clean the surface in the same cycle.
Manno discloses a developer system for reproduction and printing machines. A magnetic brush roll is used to apply developer with the print drum.
3. Solution to the Problem
None of the prior art references uncovered in the search show a device for measuring the angular relationship between the print drum axis and the magnetic brushes within the developer roll, to aid in proper angular adjustment of the magnetic brushes to optimize print quality.